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Abstract:

A method and apparatus for controlling deflection, deceleration, and
focus of an ion beam are disclosed. The apparatus may include a graded
deflection/deceleration lens including a plurality of upper and lower
electrodes disposed on opposite sides of an ion beam, as well as a
control system for adjusting the voltages applied to the electrodes. The
difference in potential between pairs of upper and lower electrodes are
varied using a set of "virtual knobs" that are operable to independently
control deflection and deceleration of the ion beam. The virtual knobs
include control of beam focus and residual energy contamination, control
of upstream electron suppression, control of beam deflection, and fine
tuning of the final deflection angle of the beam while constraining the
beam's position at the exit of the lens. In one embodiment, this is done
by fine tuning beam deflection while constraining the beam position at
the exit of the VEEF. In another embodiment, this is done by fine tuning
beam deflection while measuring the beam position and angle at the wafer
plane. In a further embodiment, this is done by tuning a deflection
factor to achieve a centered beam at the wafer plane.

Claims:

1. A method for controlling deflection of an ion beam, comprising
providing an electrode configuration comprising a plurality of upper and
lower electrode pairs, the upper and lower electrodes of each pair
positioned on opposite sides of an ion beam; grading a deceleration of
the ion beam, obtaining a deflection factor function along a length of
the lens to obtain a beam angle correction; and obtaining electrode
voltages for the plurality of upper and lower electrode pairs to adjust
the grading, the deflection factor, and a focus of the ion beam such that
a central ray trajectory (CRT) of the ion beam is positioned at a center
of the lens center; wherein adjusting the grading and deflection factor
is achieved using at least one virtual knob that adjusts at least one
parameter of the ion beam.

2. The method of claim 1, wherein the at least one virtual knob controls
the beam focus and residual energy contamination.

3. The method of claim 1, wherein the at least one virtual knob controls
an upstream electron suppression of the ion beam, preventing electrons
from being stripped from the ion beam.

4. The method of claim 1, wherein the at least one virtual knob controls
a deflection of the beam, and centers the beam at the exit of the lens.

5. The method of claim 4, further comprising measuring currents on inner
and outer final ground electrodes of the plurality of electrode pairs,
and centering the beam by varying beam deflection until the currents on
the inner and outer final ground electrodes are equal.

6. The method of claim 4, further comprising providing a collimated light
sensor vertically centered within an exit aperture of the lens to
determine beam centering.

7. The method of claim 1, wherein the at least one virtual knob controls
a final deflection angle of the ion beam and constrains the position of
the ion beam at the exit of the lens.

8. The method of claim 1, wherein the step of grading a deceleration of
the ion beam further comprises calculating the energy of the beam's
central ray trajectory (CRT) along a length of the lens.

9. The method of claim 1, wherein electrode voltages are assigned to the
upper and lower electrode pairs such that voltages of outer electrodes of
the plurality of upper and lower electrode pairs remain negative.

10. The method of claim 1, wherein an outer suppression electrode of the
plurality of electrodes remains below an upstream beamline potential.

11. A system for controlling deflection of a charged particle beam,
comprising a graded lens comprising a plurality of sets of electrodes,
each set of electrodes spaced apart by a gap to allow a charged particle
beam to pass therebetween; a controller for controlling different
combination of voltage potentials to be applied to the plurality of sets
of electrodes; and a machine readable storage medium encoded with a
computer program code such that, when the computer program code is
executed by a processor, the processor performs a method comprising:
grading a deceleration of the ion beam, obtaining a deflection factor
function along a length of the lens to obtain a beam angle correction;
and obtaining electrode voltages for the plurality of upper and lower
electrode pairs to adjust the grading, the deflection factor, and a focus
of the ion beam such that a central ray trajectory (CRT) of the ion beam
is positioned at a center of the lens center; wherein adjusting the
grading and deflection factor is achieved using at least one virtual knob
that adjusts at least one parameter of the ion beam.

12. The system of claim 11, wherein the at least one virtual knob
controls the beam focus and residual energy contamination.

13. The system of claim 11, wherein the at least one virtual knob
controls an upstream electron suppression of the ion beam, preventing
electrons from being stripped from the ion beam.

14. The system of claim 11, wherein the at least one virtual knob
controls a deflection of the beam, and centers the beam at the exit of
the lens.

15. The system of claim 14, further comprising instructions for measuring
currents on inner and outer final ground electrodes of the plurality of
electrode pairs, and centering the beam by varying beam deflection until
the currents on the inner and outer final ground electrodes are equal.

16. The system of claim 14, further comprising instructions for providing
a collimated light sensor vertically centered within an exit aperture of
the lens to determine beam centering.

17. The system of claim 11, wherein the at least one virtual knob
controls a final deflection angle of the ion beam and constrains the
position of the ion beam at the exit of the lens.

18. The system of claim 11, wherein the step of grading a deceleration of
the ion beam further comprises calculating the energy of the beam's
central ray trajectory (CRT) along a length of the lens.

20. The system of claim 11, wherein electrode voltages are assigned to
the upper and lower electrode pairs such that voltages of outer
electrodes of the plurality of upper and lower electrode pairs remain
negative.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] Embodiments of the invention relate to the field of ion
implantation for forming semiconductor structures. More particularly, the
present invention relates to a method for controlling deflection of a
charged particle beam within a graded electrostatic lens.

[0003] 2. Discussion of Related Art

[0004] Ion implanters are widely used in semiconductor manufacturing to
selectively alter conductivity of materials. In a typical ion implanter,
ions generated from an ion source are directed through a series of
beam-line components that may include one or more analyzing magnets and a
plurality of electrodes. The analyzing magnets select desired ion
species, filter out contaminant species and ions having undesirable
energies, and adjust ion beam quality at a target wafer. Suitably shaped
electrodes may modify the energy and the shape of an ion beam.

[0005] FIG. 1 shows a conventional ion implanter 100 which comprises an
ion source 102, extraction electrodes 104, a 90° magnet analyzer
106, a first deceleration (D1) stage 108, a 70° magnet analyzer
110, and a second deceleration (D2) stage 112. The D1 and D2 deceleration
stages (also known as "deceleration lenses") are each comprised of
multiple electrodes with a defined aperture to allow an ion beam to pass
therethrough. By applying different combinations of voltage potentials to
the multiple electrodes, the D1 and D2 deceleration lenses can manipulate
ion energies and cause the ion beam to hit a target wafer at a desired
energy.

[0006] The above-mentioned D1 or D2 deceleration lenses are typically
electrostatic triode (or tetrode) deceleration lenses. FIG. 2 shows a
perspective view of a conventional electrostatic triode deceleration lens
200. The electrostatic triode deceleration lens 200 comprises three sets
of electrodes: entrance electrodes 202 (also referred to as "terminal
electrodes"), suppression electrodes 204 (or "focusing electrodes"), and
exit electrodes 206 (also referred to as "ground electrodes" though not
necessarily connected to earth ground). A conventional electrostatic
tetrode deceleration lens is similar to the electrostatic triode
deceleration lens 200, except that a tetrode lens has an additional set
of suppression electrodes (or focusing electrodes) between the
suppression electrodes 204 and the exit electrodes 206. In the
electrostatic triode deceleration lens 200, each set of electrodes may
have a space/gap to allow an ion beam 20 to pass therethrough (e.g., in
the +z direction along the beam direction). As shown in FIG. 2, each set
of electrodes may include two conductive pieces electrically coupled to
each other to share a same voltage potential. Alternatively, each set of
electrodes may be a one-piece structure with an aperture for the ion beam
20 to pass therethrough. As such, each set of electrodes are effectively
a single electrode having a single voltage potential. For simplicity,
each set of electrodes are herein referred to in singular. That is, the
entrance electrodes 202 are referred to as an "entrance electrode 202,"
the suppression electrodes 204 are referred to as a "suppression
electrode 204," and the exit electrodes 206 are referred to as an "exit
electrode 206."

[0007] In operation, the entrance electrode 202, the suppression electrode
204, and the exit electrode 206 are independently biased such that the
energy and/or shape of the ion beam 20 is manipulated in the following
fashion. The ion beam 20 may enter the electrostatic triode deceleration
lens 200 through the entrance electrode 202 and may have an initial
energy of, for example, 10-20 keV. Ions in the ion beam 20 may be
accelerated between the entrance electrode 202 and the suppression
electrode 204. Upon reaching the suppression electrode 204, the ion beam
20 may have an energy of, for example, approximately 30 keV or higher.
Between the suppression electrode 204 and the exit electrode 206, the
ions in the ion beam 20 may be decelerated, typically to an energy that
is closer to the one used for ion implantation of a target wafer. In one
example, the ion beam 20 may have an energy of approximately 3-5 keV or
lower when it exits the electrostatic triode deceleration lens 200.

[0008] The significant changes in ion energies that take place in the
electrostatic triode deceleration lens 200 may have a substantial impact
on a shape of the ion beam 20. For example, the deceleration lens 200,
which may provide co-local deflection for filtering energetic neutrals,
may face challenges associated with control of deflection angle and beam
focus. Voltage needed to control deflection of the ion beam 20 may depend
on the energy of the beam (e.g., both input and output), whereas voltage
to control focus of the ion beam 20 may be varied to accommodate ion
beams with different current and height. This may lead to difficulty in
tuning the ion beam 20 since tuning the size of the ion beam 20 (focus)
may not be readily feasible if a position of the ion beam 20 also
continues to vary. Conventional systems and methods do not provide a
solution for independently controlling the deflection and/or focus of an
ion beam in a co-locally deflecting and decelerating lens. In view of the
foregoing, it may be understood that there are significant problems and
shortcomings associated with current ion implantation technologies.

SUMMARY OF THE INVENTION

[0009] A method is disclosed for assigning electrode voltages within a
decel/deflect lens which maintains an arcuate motion of the beam,
matching the symmetry of the graded decel/deflect lens. Small adjustment
of deflect angle is accomplished smoothly, via small adjustments of the
voltages throughout lens, rather than abruptly at end of lens. The
vertical position can be constrained at the exit of the lens, or at the
wafer plane, allowing the position and angle of the beam at the wafer to
be tuned independently. Several methods of incorporating beam vertical
position detection within the Vertical Electrostatic Energy Filter (VEEF)
are disclosed.

[0010] A method is disclosed for controlling deflection of an ion beam,
comprising: providing an electrode configuration comprising a plurality
of upper and lower electrode pairs, the upper and lower electrodes of
each pair positioned on opposite sides of an ion beam; grading a
deceleration of the ion beam, obtaining a deflection factor function
along a length of the lens to obtain a beam angle correction; and
obtaining electrode voltages for the plurality of upper and lower
electrode pairs to adjust the grading, the deflection factor, and a focus
of the ion beam such that a central ray trajectory (CRT) of the ion beam
is positioned at a center of the lens center; wherein adjusting the
grading and deflection factor is achieved using at least one virtual knob
that adjusts at least one parameter of the ion beam.

[0011] A system for controlling deflection of a charged particle beam,
comprising: a graded lens comprising a plurality of sets of electrodes,
each set of electrodes spaced apart by a gap to allow a charged particle
beam to pass therebetween; and a controller for controlling different
combination of voltage potentials to be applied to the plurality of sets
of electrodes, a machine readable storage medium encoded with a computer
program code such that, when the computer program code is executed by a
processor, the processor performs a method. The method comprises: grading
a deceleration of the ion beam, obtaining a deflection factor function
along a length of the lens to obtain a beam angle correction; and
obtaining electrode voltages for the plurality of upper and lower
electrode pairs to adjust the grading, the deflection factor, and a focus
of the ion beam such that a central ray trajectory (CRT) of the ion beam
is positioned at a center of the lens center; wherein adjusting the
grading and deflection factor is achieved using at least one virtual knob
that adjusts at least one parameter of the ion beam.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings illustrate preferred embodiments of the
disclosed method so far devised for the practical application of the
principles thereof, and in which:

[0029] To solve the problems with conventional lens configurations, an
improved electrostatic lens configuration may include one or more
variable-control suppression/focusing electrodes. These electrodes may
include a variety of shapes, curvatures, positions, materials, and/or
configurations that are independently or separately controlled/biased
with respect to one another thereby providing flexible and effective
manipulation of an ion beam's shape as well as its energy.

[0030] FIG. 3 depicts a side view of an exemplary graded lens
configuration 300. The graded lens configuration 300 may include several
sets of electrodes. For example, the graded lens configuration may
include a set of entrance electrodes 302, one or more sets of
suppression/focusing electrodes 304, and a set of exit electrodes 306.
Each set of electrodes may have a space/gap to allow an ion beam 30
(e.g., a ribbon beam) to pass therethrough.

[0031] In some embodiments, these electrodes (e.g., entrance electrode
302, suppression/focusing electrodes 304, and the exit electrode 306) may
be provided in a housing 308. A pump 310 may be directly or indirectly
connected to the housing 308. In one embodiment, the pump 310 may be a
vacuum pump for providing a high-vacuum environment or other controlled
environment. In other embodiments, the housing 308 may include one or
more bushings 312. These bushings 312 may be used to electrically isolate
the housing 308 from other components. Other various embodiments may also
be provided.

[0032] As shown in FIG. 3, each set of entrance electrodes 302 and exit
electrodes 306 may include two conductive pieces electrically coupled to
each other or may be a one-piece structure with an aperture for the ion
beam 30 to pass therethrough. In some embodiments, upper and lower
portions of suppression/focusing electrodes 304 may have different
potentials (e.g., in separate conductive pieces) in order to deflect the
ion beam 30 passing therethrough. For simplicity, each set of electrodes
may be referred to in singular. That is, the entrance electrodes 302 may
be referred to as an "entrance electrode 302," the suppression/focusing
electrodes 304 may be referred to as a "suppression/focusing electrode
304," and the exit electrodes 306 may be referred to as an "exit
electrode 306." Although the graded lens configuration 300 is depicted as
a seven (7) element lens configuration (e.g., with five (5) sets of
suppression/focusing electrodes 304), it should be appreciated that any
number of elements (or electrodes) may be utilized. For example, in some
embodiments, the graded lens configuration 300 may utilize a range of
three (3) to ten (10) electrode sets. Other various embodiments may also
be provided. In some embodiments, the ion beam 30 passing through the
electrodes may include boron or other elements. Electrostatic focusing of
the ion beam 30 may be achieved by using several thin electrodes (e.g.,
the suppression/focusing electrodes 304) to control grading of potential
along an ion beam path or beamline 30. In the graded lens configuration
300, high deceleration ratios may also be provided while avoiding
over-focusing.

[0033] As a result, use of input ion beams 30 may be used in an energy
range that may enable higher quality beams, even for very low energy
output beams. In one embodiment, as the ion beam 30 passes through the
electrodes of the lens configuration 300, the ion beam 30 may be
decelerated from 6 keV to 0.2 keV and deflected at 15° by the
electrodes of the graded lens configuration 300. In this example, the
energy ratio may be 30/1. Other various embodiments may also be provided.

[0034] It should be appreciated that separating and independently
controlling deceleration, deflection, and/or focus may be accomplished
by: (1) maintaining symmetry of electrodes (e.g., the entrance electrode
302, suppression/focusing electrodes 304, and the exit electrode 306)
with respect to a central ray trajectory ("CRT") of the ion beam 30, and
(2) varying deflection voltages along the CRT of the ion beam 30 to
reflect beam energy at each point along the CRT at a deflection angle 35.
By symmetry of the electrodes with respect to the CRT of the ion beam 30,
it should be appreciated that the ends of upper and lower electrodes
closest to the ion beam 30 may be maintained at equal (or near equal)
perpendicular distances from the CRT of the ion beam 30. For example, a
difference in voltages on electrodes above and below the ion beam 30
(e.g., Vdef(z)=Vupper(z)-Vlower(z)) may be configured so
that a deflection component of the electric field (e.g.,
(Vupper(z)-Vlower(z))/gap(z)) may be a fixed ratio/factor of
the beam energy at that point (which may vary along the electrodes or
lenses) (e.g., factor*Ebeam(z)). For example, this may be expressed
as Equation 1 below:

Vdefl(z)/gap(z)=factor*Ebeam(z) Eq. 1

[0035] In some embodiments, this deflection voltage may be applied
anti-symmetrically above and/or below (e.g., +/-Vdefl(z) relative to
the potential at the crt at that z). In other embodiments, for example,
the deflection voltage may be applied to just one side of the ion beam 30
with twice the deflection voltage. It should be appreciated that since
the relationship between the top and bottom electrode voltage may be
fixed for a given geometry, it may be possible to implement this
relationship in a circuit network or other similar network. Accordingly,
a need for doubling the number of power supplies and/or fixing this
relationship in hardware may be reduced, if not completely eliminated.
Other various embodiments may also be provided.

[0036] FIGS. 4A-4D depict illustrative graphs 400A-400D of deflection,
deceleration, and/or focus in a graded lens configuration in accordance
with the exemplary embodiment of FIG. 3. In these illustrative graphs
400A-400D, the ion beam 30 may be depicted with differing emittance and
voltages/bias at each electrode producing various focus conditions. It
should be appreciated that each exemplary graph may use a deflection
factor (as described above in Eq. 1) of 0.16 and may produce the same or
similar a deflection (e.g., deflection of 20°). For example, FIG.
4A depicts an illustrative graph 400A of deflection, deceleration, and/or
focus in a graded lens configuration using a zero (0) emittance ion beam,
FIG. 4B depicts an illustrative graph 400B of deflection, deceleration,
and/or focus in a graded lens configuration using a non-zero emittance
ion beam, FIG. 4c depicts an illustrative graph 400C of deflection,
deceleration, and/or focus in a graded lens configuration using a
non-zero emittance ion beam with convergence, and FIG. 4D depicts an
illustrative graph 400D of deflection, deceleration, and/or focus in a
graded lens configuration situations, using different focus voltages. In
most situations, the deflection factor of Eq. 1 may be maintained as
0.16. Other various embodiments may also be provided.

[0037] It will also be appreciated that other graded lens configurations
may be provided, such as those disclosed in co-pending application Ser.
No. 12/348,091, filed Jan. 2, 2009, titled, "Techniques for Independently
Controlling Deflection, Deceleration and Focus of an Ion Beam," docket
no. 2008-109, the entirety of which application is incorporated by
reference herein.

[0038] As noted, a graded deceleration-deflect electrostatic lens contains
many electrodes, each connected to separate power supplies. For example,
a 7-stage lens will typically require 10 high voltage power supplies (in
addition to the main deceleration supply). The electrode voltages must be
varied together to achieve: (1) grading of the deceleration to control
beam focus; (2) centering of the beam's central ray trajectory (CRT) on
the lens center line, (3) adjustment of the beam's final deflection
angle; and (4) minimization of energy contamination.

[0039] The above should be achieved while maintaining the constraint that
all electrode voltages remain negative with respect to the upstream
beam-line to prevent electron currents.

[0040] Controlling this large number of power supplies is a significant
controls challenge. A method is therefore disclosed for combining these
power supply controls to yield a small number of "virtual knobs" that
directly reflect the goals stated above. Such a re-parameterization
simplifies, and enables the control of, this complex device.

[0041] The disclosed method refers to assigning voltages to the electrodes
of an electrostatic lens capable of independently decelerating and
deflecting an ion beam (also referred to as a "Vertical Electrostatic
Energy Filter", or VEEF). This geometry, which is shown schematically in
FIG. 5 contains 7 inner and outer electrodes (numbered 0 through 6),
centered about a 20-degree deflection arc θ. In this example, the
positions of the electrodes are fanned (so that high energy neutrals from
the input beam will not hit the high voltage electrodes), and the angular
spacing of the electrodes is uniform. The first electrodes "0" (inner and
outer) are tied to the upstream (high energy) beamline, and the last
electrodes "6" (inner and outer) are tied to the downstream (low energy
beamline). The difference in potential between the upstream and
downstream beamlines is the deceleration voltage of the lens. In the
disclosed embodiment, there are additionally 10 other power supplies
connected to the other electrodes, the difference in voltage between the
inner and outer electrodes (at a particular position along the deflection
arc) is proportional to the energy of the beam's CRT at that point. The
constant of proportionality between the deflection voltage difference and
the CRT energy is referred to as the deflection factor Fdefl.

[0042] The techniques for assigning voltages to such a graded
deflect/decel electrostatic lens or VEEF involves several aspects:

[0043] 1. A method for assigning electrode voltages (based on a few
"virtual knobs") [0044] a. Grading the deceleration, which entails
calculating the energy of the beam's CRT along the lens, [0045] b.
Calculating the deflection factor function along the lens to achieve an
angle correction (beyond the geometric angle of the lens geometry),
[0046] c. Calculating the electrode voltages to achieve the graded
deceleration and deflection with angle correction in such a way that the
beam CRT remains close to lens center, while maintaining all voltages
negative (relative to the downstream beamline), [0047] 2. An apparatus
for discerning the vertical position of the beam at the exit of the VEEF;

[0048] 3. A method for tuning these "virtual knobs" to achieve the desired
deflection and focus, while maintaining the beam CRT centered within the
lens.

[0049] Each of the above will now be described in turn.

[0050] 1. Method for Assigning Electrode Voltages

[0051] a. Grading the Deceleration

[0052] The first electrode not tied to the input beamline (numbered 1 in
FIG. 5) is known as the suppression electrode, as it suppresses upstream
beam plasma electrons from being stripped from the beam. Between this
suppression electrode and the final ground electrode, the energy of the
beam is reduced according to the potentials on the electrodes 2-5. This
grading of the deceleration field affects the net focus of the beam, as
well as the residual energy contamination (EC). According to the
disclosed method, this grading is described by a power law, embodied by a
single parameter, alpha, as defined by Eq. 2 below

where i=index describing the location along the lens, Ecrt=Energy of
ions on the crt at each point I, Ef=final energy of the beam,
E0=initial energy of the beam, Vs=potential on the crt at the
location of the suppression electrode, and e=charge of electron.

[0053] Thus, from Eq. 2, if α=1, the energy of the ions on the crt
varies linearly from E0+eVs to Ef, whereas if
α>1, the energy drops more quickly, as exemplified in FIG. 6. In
general, a large a decelerates the beam quickly, reducing the chance of
high energy neutralized ions from reaching the wafer (i.e. resulting in
low EC), while a small a results in greater focusing of the beam.

[0054] b. Deflection Angle Correction

[0055] Arcuate Motion

[0056] The difference in voltage between the inner and outer electrodes
provides an electric field perpendicular to the particle's motion,
therefore producing a localized circular, or arcuate motion (see FIG. 7).
The radius of curvature and length of the arc (and therefore the net
deflection angle) must conform to the geometry of the lens in order for
the beam to remain centered between the inner and outer electrodes,
thereby minimizing aberrations and the coupling between focus and
deflection.

[0057] If Fdefl is constant over the length of the VEEF, the beam's
central ray trajectory (CRT) would be perfectly circular, resulting in a
net deflection angle θ over its length L. It is desirable to be
able to fine tune the net deflection angle to accommodate variations in
input beam alignment and effects of space-charge, while causing minimum
deviation from this arcuate motion. According to the method of this
invention, this is done by adjusting the radius of curvature of the
beam's deflection linearly along the length of the lens. Thus the single
parameter Fdefl is replaced by 2 parameters: the average value
fav and the slope β of Fdefl. (See FIG. 8 and Eq. 3 below)

F defl ( z ) = f 0 + β z =
f av - β L 2 + β z Eq . 3
##EQU00002##

[0058] At each point along the deflection path, the differential
deflection is

[0062] FIGS. 9A and 9B show ion beam trajectories through a VEEF,
demonstrating the affect of varying fav and β over a lens of
length L=150 mm. Varying fav alone affects both the final angle as
well as position of the beam, while varying β alone affects only the
position, leaving the final angle invariant.

[0063] By varying both fav and β together, the net deflection
angle can be varied while leaving the vertical position invariant at some
point along the beam's trajectory Zc. The required constraint
between fav and β to achieve this can be found by considering
the total differentials:

[0064] Constraining the position at the exit of lens (dy(L)=0), one
obtains the relationship between a desired change in the net deflection
angle θ (dθ), and the needed changes in fav and β
(dfav, dfav):

[0065] Thus, F0 (=fav when β=0) and
θcor(=dθ in eq. 11), can be specified such that if the
deflection takes place between electrodes 2-6 within the VEEF (FIG. 4),
the deflection Fdefl(i) factor at the location of these electrodes
would be:

[0066] FIG. 10 shows different beam paths with varied θcor (dth
in FIG. 10), with y constrained at the VEEF exit (L=300 mm in the
figure).

[0067] Alternatively, the position can be constrained further downstream
(e.g., a distance D) from the exit of the VEEF while changing the net
deflection within the VEEF by dθ, which translates to moving the
position at the exit of the VEEF by -dθD.

[0069] FIG. 11 shows different beam paths with varied de, with y
constrained at a distance D from lens exit.

[0070] c. Assigning the Deflection Potentials

[0071] After specifying the F0 and θcor (along with the
appropriate constraint--y at exit or y at wafer), the electrode voltages
are assigned on the upper and lower electrodes to achieve the desired
arcuate motion. As was shown in FIG. 7, the electrode voltages are
determined by the deflection factor at that position along the beam's
CRT, according to:

where Vcrt is calculated according to Eq. 2, using
Vcrt=Ef-Ecrt. However, according to Eq. 16, it is possible
for the outer electrodes to go positive, which can cause a failure of
electron suppression (causing beam blow-up before or after the
deceleration lens), as is exemplified in FIG. 12, which shows how the
outer electrode potentials at the end of the VEEF can become positive,
thereby stripping electrons from the downstream beam plasma.

[0074] 2. The outer suppression electrode remains below the upstream
beamline potential. (This can also be a requirement of the power supply
architecture, since the suppression supply is generally referenced to the
upstream beamline.)

[0075] Constraint 1 can be satisfied by subtracting a fixed potential,
δV, along the CRT (at every point). Since δV increases the
energy of the beam, it is calculated to satisfy the following condition:

[0076] δV is subtracted from Vcrt obtained from Eq. 2, and the
upper and lower electrode voltages are calculated according to Eq. 13.

[0077] Constraint 2 can be satisfied by specifying the outer suppression
voltage to be greater than 0, rather than specifying the suppression
voltage on the CRT. That is, Eq. 13 can be used to calculate Vs,crt
from the specified Vs,upper. Note that one usually specifies a
(positive) suppression power supply value V.sub.S,VF, which is referenced
to V0 (the potential of the upstream beam line); i.e.
V.sub.S,VF≡V0-Vs,upper.

[0078] This calculated Vs,crt is used in the alpha algorithm to
specify Ecrt (note Vs,crt=Vcrt(1)=V0-Ecrt(1)).

[0079] Virtual Knobs

[0080] For a specified input beam to the decel/deflect lens, and specified
energy deceleration of the lens, the power supplies that control the
potentials on the electrodes within the lens control the focus and
deflection of the beam. According to the disclosed method, these power
supplies are controlled by the following "virtual knobs":

[0081] (1) Alpha--controls the beam's focus, as well as residual energy
contamination;

[0082] (2) Vs--controls the upstream electron suppression, preventing
electrons from being stripped from the upstream beam;

[0083] (3) F0--controls the deflection of the beam, used to center
the beam at the exit of the lens (with θcor=0);

[0084] (4) θcor--provides fine-tune of the final deflection
angle of the beam while constraining the position at the exit of the lens

[0085] 2. Apparatus for Centering Beam at Exit of Deflect Lens

[0086] It would be advantageous to be able to tune F0 in order to
center the beam at the exit of the deflect lens. Such dynamic tuning may
be important due to slight variations in the alignment of the input beam,
and effects of space charge.

[0087] Approach 1: Use Final Ground Electrodes as Current Sensors

[0088] By measuring the currents on the inner and outer final ground
electrodes, the beam can be centered by varying F0 until Ii and
I0 are equal (see FIG. 13). If the beam is too narrow to produce
current on both final ground electrodes, F0 can be varied until the
two values of F0 that achieve the same current on the electrodes is
reached, and then set F0 between these two values.

[0090] An ion beam travelling through residual gas produces light (as the
residual gas molecules are excited and relax back their ground states).
This can be used to measure the vertical position of the beam.

[0091] As shown in FIG. 14, The light sensor can be made very sensitive by
employing CCD (charge-coupled device) or ICCD (intensified charge-coupled
device) which can be capable of "single photon" detection. A
1-dimensional array of CCDs can be used to obtain the vertical profile of
the beam. By taking the image without the beam, any background light (for
example from a downstream plasma flood gun) could be subtracted out.

[0092] 3. Methods for Tuning the "Virtual Knobs"

[0093] Method 1: Using θcor with Constrained Position at Exit
of VEEF

[0094] The deceleration ratio, α, and Vs, are set to achieve
the desired energy, current, and focus of the final beam. The process for
determining these values are described in U.S. patent application Ser.
No. 12/348,091, filed Jan. 2, 2009, titled, "Techniques for Independently
Controlling Deflection, Deceleration and Focus of an Ion Beam." The
Fo parameter is set to achieve a centered beam at the exit of the
VEEF. This is done by tuning F0 while discerning the vertical
position of the beam at the exit of the VEEF using one of the two
approaches described above (current sensors on final ground electrodes,
or centered light sensor). Once this it done, the beam can then be
centered at the wafer plane using θcor (with vertical position
constrained at the exit of VEEF). This ensures that the beam is both
centered at the exit of the VEEF and that the VEEF is excited at the
correct angle (i.e. the bend angle at which the beamline is set). The
centering of the beam at the wafer plane is accomplished using a
two-dimensional profiler, or other known technique for sensing the
vertical position of the beam.

[0095] Method 1a: Using θcor with Constrained Position at Exit
of VEEF and Measuring Both Position and Angle at the Wafer Plane

[0096] It is advantageous to use the parameter θcor (with
constrained position at exit of VEEF) to tune the position of the beam
even if the vertical position of the beam is not directly discerned at
the exit of the VEEF. Two parameters are measured to be able to set both
θcor and F0 to their optimal values. In this method, both
the beam's average vertical position Y and average vertical angle Y' are
measured at the wafer plane. The response or sensitivities of these
parameters to varying θcor and F0 are shown for a
particular case in FIGS. 15A and 15B, and can clearly be seen to be
linear.

[0097] The partial derivatives can be determined experimentally with just
3 points.

[0101] Method 2: Using θcor with Constrained Position at the
Wafer Plane

[0102] The deceleration ratio, α, and Vs, are set to achieve
the desired energy, current, and focus of the final beam. F0 is then
tuned to achieve a centered beam at the wafer plane (accomplished using a
two-dimensional profiler, or other known means of sensing the vertical
position of the beam). The angle of the beam can then be tuned at the
wafer plane to be the specified bend angle by varying θcor
(with vertical position constrained at the wafer plane). This ensures
that the beam is both centered at the exit of the VEEF and exiting the
VEEF at the correct angle.

[0103] 1. Application of the Disclosed Tuning Method to Other Lens
Geometries

[0104] It will be appreciated that the disclosed method is not limited in
application to any one specific lens geometry. Rather, it can be applied
to applications using a variety of different lens geometries.

[0105] For any electrostatic lens combining deceleration and deflection,
whether there is a single or a multiplicity of bends, it is important
that the beam remain centered at the exit of the lens (where the focus is
the largest) for several reasons:

[0106] (1) it minimizes aberrations,

[0107] (2) it reduces the interaction between angle adjustment and focus;
and

[0109] Consider the example of a "chicane lens", exemplified in FIG. 16.
Since the final deceleration occurs while the beam is still being
deflected, there will always be residual energy contamination due to
neutrals forming within the final bend. In order to perform an adjustment
of the exit beam angle, the radius of curvature of the final bend needs
to be adjusted. It would be desirable to do this while maintaining the
exit position of the beam, which would minimize any variation in neutral
trajectories reaching the wafer. This could be accomplished by applying
independent potentials on several of the final electrodes (and perhaps
adding more electrodes), accomplishing simultaneous grading and
deflection of the beam, and allowing the application of the tuning method
described herein.

[0110] While the present invention has been disclosed with reference to
certain embodiments, numerous modifications, alterations and changes to
the described embodiments are possible without departing from the sphere
and scope of the present invention, as defined in the appended claims.
Accordingly, it is intended that the present invention not be limited to
the described embodiments, but that it has the full scope defined by the
language of the following claims, and equivalents thereof.

[0111] The method described herein may be automated by, for example,
tangibly embodying a program of instructions upon a computer readable
storage media capable of being read by machine capable of executing the
instructions. A general purpose computer is one example of such a
machine. A non-limiting exemplary list of appropriate storage media well
known in the art includes such devices as a readable or writeable CD,
flash memory chips (e.g., thumb drives), various magnetic storage media,
and the like.

[0112] The functions and process steps herein may be performed
automatically or wholly or partially in response to user command. An
activity (including a step) performed automatically is performed in
response to executable instruction or device operation without user
direct initiation of the activity.

[0113] It will be appreciated that the systems and methods disclosed are
not exclusive. Other systems and methods may be derived in accordance
with the principles of the invention to accomplish the same objectives.
Although this invention has been described with reference to particular
embodiments, it is to be understood that the embodiments and variations
shown and described herein are for illustration purposes only.
Modifications to the current design may be implemented by those skilled
in the art, without departing from the scope of the invention. The
processes and applications may, in alternative embodiments, be located on
one or more (e.g., distributed) processing devices accessing a network
linking the elements of the disclosed system. Further, any of the
functions and steps provided in the Figures may be implemented in
hardware, software or a combination of both and may reside on one or more
processing devices located at any location of a network linking the
elements of the disclosed system or another linked network, including the
Internet.